1. Field of the Invention
The present invention relates to burners which burn liquid or gaseous fuels that are used, for example, in various kinds of furnaces, and in particular it relates to burners with a structure which makes it possible to greatly reduce the formation of nitrogen oxides (NOx) in the burning process.
2. Description of the Prior Art
It already is known that, in general, the higher the flame temperature becomes with a burner, the greater the undesired formation of nitrogen oxides (NOx) byproduct. Therefore, as a method for reducing NOx formation, it has been attempted to restrain the increase in the flame temperature by a method wherein the amount of excess air is reduced, i.e., so as to approach the theoretical mixture ratio, or else the exhaust gas is recycled and mixed into combusting air.
On the other hand, it has also been recognized that a circulating swirl of combusting flame has a great effect in reducing NOx formation. As a method of operation using this technique, a construction of burner has been employed wherein a combustion gas (or furnace gas) is circulated by the injection energy of the air such that a circulating swirl is created.
In this type of this construction, however, there are drawbacks in that, for example, the structure of the burner is generally complicated. Also the section of refractory structure at a high temperature has many problems, and the heat transfer efficiency is lowered by the highly raised pressure of combusting air and the slowdown of combustion, and further B, C heavy oils are not suitable for use as fuels from a structural point of view. Thus a suitable structure which has a reduction effect on NOx gas production has not been yet devised.
An object of the present invention is to provide a burner which has a very simple structure and which reduces the generation of undesirable NOx gases.
That is to say, the first object of the present invention is the provision of a burner wherein an efficient circulating swirl phenomenon is created in a flame combustion section to markedly depress NOx gas production by injecting air while it is in swirling motion, and the second object is to the provision of a burner which has a very simple structure, which is durable and easy in its manufacture, which is durable in use or maintenance, easily inspected, and so on.